Amplitude modulation of magnetrons



NQV- 27, l9,51 H. F.`ENGELMANN` 2,576,108

AMPLITUDE MODULATION 0F MAGNETRONS Filed April 14, 1948 WL T465 ATTORNEY Patented Nov. 27, 1951 AMPLITUDE MODULATION OF MAGNETRONS Herbert F. Engelmann, Mountain Lakes, N. J.,

assigner by mesne assignment to International Standard Electric Corporation,

New

York, N. Y., a corporation of Delaware Application April 14, 1948, Serial No. 21,07 0

8 Claims.

My invention relates to electron discharge devices of the magnetron type and more particularly to magnetrons adapted for amplitude modulation.

Many attempts have been made to amplitude modulate a magnetron with the result that the power output is discontinuous rather than a linear variation with respect to modulating voltage. This is certainly true when it is attempted to apply the modulating voltage in series with the anode voltage, or for that matter, to use the familiar scheme of current modulation whereby the current through the magnetron is varied. In both of these schemes, the magnetron will not operate successfully over Wide variations in current or voltage, since certain fundamental parameters which were used in designing the magnetron, will be violated.

An object of my invention is to provide a magnetron the power output of which is a linear variation with respect to a modulating voltage.

A still further object of my invention is to provide a magnetron of the interdigital type, the power output of which is a linear variation with respect to a modulating voltage.

I have found by operating the magnetron in the usual fashion, that is, optimum voltage and current, and then applying the modulation voltage to an insulated set of vanes or digits, it is possible to amplitude modulate the magnetron over a Wide range.` This scheme was tried experimentally with a Sylvania interdigitated magnetron operating at 4800 megacycles (SD 849B) Therefore, according to my invention, I provide a magnetron of the cavity resonator type or the interdigital type in which a plurality of anode vanes or digits are mounted in a circle about the cathode, adjacent one of said vanes or segments are insulated from one another for low frequencies and means are provided for applying a modulating voltage between adjacent ones of said vanes or segments of the resonator.

The above mentioned objects and features will be more clearly understood and others will be* come apparent to those skilled in the art by reference to the following description and the drawing of which:

Fig. 1 shows a vertical cross-sectional view of a magnetron of the interdigital type incorporating a feature of my invention and Fig. 2 shows a horizontal cross-sectional view of a modified magnetron of the cavity resonator type incorporating features of my invention.

In the drawing there is shown a magnetron comprising an evacuated cavity resonator I, a

vhollow cathode 2 in the center of the cavity resonator heated by an interiorly located thermionic lament 3, and an anode structure consisting of an even number of short length identical anode segments ll. A coil 5 associated with iron pole pieces 6 and 1 produces a magnetic iield whose flux lines extend parallel to the cathode.

Ultra high frequency oscillations are taken out of the magnetron by means of an output coupling loop 8 which is coupled to utilization apparatus, such as a transmission line leading to an antenna, not shown. One end of the loop 8 is shown coupled to one wall of the cavity resonator While the other end extends externally through a glass seal The cathode heater leads and the cathode lead extends out from the magnetron through glass seal I0. The heater 3 may be embedded in high temperature insulating material inside hollow cathode 2 after the usual manner of constructing indirectly heated cathodes. The central outside surface of cathode 2 may be oxide coated according to common practice. The ends of the cathode 2 are provided with flanges which act as shields to help conne electrons to the central I portion of the device.

The anode segments 4 may be any even number of segments, preferably six or eight, and lie in a circle around the cathode. Those portions of these anode segments upon which the electrons impinge are thicker than the short stubs which connect these segments to the oppositely disposed faces of the resonator, as shown.

The anode segments 4 are mounted on opposite walls II and I2 of the cavity resonator I. Alternate ones of said segments are mounted on one wall and adjacent ones of said segments are mounted on opposite walls. Walls II and I2 are insulated from one another by an annular insulator lug I3 forming a bi-pass condenser with the sections of the wall. The magnetic pole pieces are also separated from the walls of the resonator I by annular rings of insulation I4 and I 5 in order that the magnetic circuit does not short circuit the by-pass condenser I3.

In the preferred embodiment, one part of the resonator I is grounded and the modulating volt" age source I6 coupled between ground and the part of Wall I 2 which is insulated from the rest of the resonator by insulating ring I3 and which carries one set of the anode segments 4.

If it is desired to operate the magnetron under pulse conditions a source of negativ e pulses I1 for pulse modulation is connected between ground and the cathode 2.

In an experimental test it was found that the -sections being radial.

- the envelope I8.

power output from an interdigital magnetron operating at 4000 megacycles, amplitude modulated according to this disclosure, wasY a linear function of the modulating voltage.

The same arrangement isapplicable to cavity .magnetrons in which the cavities are formed by vanes arranged radially about the cathode. A1- ternate vanes about said cathode are insulated from the other vanes-and electrically connected and the modulating voltage is applied thereto. The one set of vanes should be insulated from the other by a built in mica or similar condenser which will by-pass the radio frequency.

As illustrated in Fig. 2, an envelope I8 which is made of a block of conductive material is provided with a central bore i9 within which is mounted Va cathode axially with the outer.

and it has been found that the output from the magnetron is modulated in amplitude linearly Y with respect to said modulating voltage.

The invention is not intended to be limited to Ythe specic embodiments described in detail above and other applications will be apparent to those skilled in the art.

I claim:

1. A magnetron adapted for amplitude modulation ccmprisinga cavity resonator, a cathode mounted inside said resonator, an even number of anode segments greater than two mounted in a circle about said cathode, means insulating adjacent segments from one another, means connecting alternate segments together, and means for applying a modulating signal between adjacentcnes of said segments.

resonator at right angles to said surfaces, an anode structure surrounding said cathode and composed of Van evenrnumber of anode segments greater than two located between said surfaces and mounted with alternate segmentsY on the same surface, adjacent segments being mounted number of vanes mounted to extend from said envelope radially towards said cathode, insulating means separating alternate ones of said vanes from saidl envelope, means electrically inter-connecting said alternatev ones of said vanes, the others of said vanes being conductively connected to said envelope, and means for applying a modulating voltage between adjacent -ones of said vanes.

4. A magnetron according to claim 3 wherein Y said insulating means comprises a high-'freon opposite ones of said two ysurfaces of said resonator, means adjacent said resonator for producing a magnetic field having flux lines eX- tending in a direction substantially parallel to said cathode, and means for applying a potential signal between said parallel surfaces for amplitude modulating the oscillations in said resonator.

6. A magnetron adapted for amplitude modu-k lation comprising a cavity resonator composed of a substantially closed metal wall having two parallel surfaces for maintaining radio frequency oscillations, a cathode mounted inside said resohaving flux lines extending in a direction substantially parallel to said cathode, anda radio requency by-pass condenser separating said two surfaces from one another for low frequencies, and means electrically coupled between said two surfaces for applying a potential signal therebetween for amplitude modulating the oscillation in said resonator.

7. A magnetron according to claim 1 wherein the cavity resonator is deiined at least in part by two opposed wall portions, one group of alternate anodesegments being supported' on one wall portionand the other group 4of alternate anode segments being supported on the other wall portion, and the means for insulating adjacent segments include insulation disposed .between said wall portions.

8. A magnetron according to claim 1 wherein the cavity resonator is dened at least in part by a circular wall, the anode segments being disposed radially inwardly of said wall, and the means for insulating adjacent segments includes insulation disposed between alternate segments and said wall.

HERBERT F. ENGELMANN.

REFERENCES CTED `The followingr references are oi record inthe le of this patent:

Y UNiTaD sTATEs PATENTS Number Name Date 2,128,237 Dallenbach Aug. 30, 1938 2,152,035 Fritz et a1. Mar. 28, 1939 V 2,424,886 Hansell July 29,1947 2,432,466 Burns .Dec. 9, 1947 2,462,869 Kather Mar. 1, 1949 2,478,644 Spencer Aug. 9, 1949 

